Io; flux tube; ultraviolet spectroscopy; Jupiter; electron energy; slippage
Abstract :
[en] [1] Spectral observation of both polar regions of Jupiter in the far ultraviolet (FUV) obtained with the Space Telescope Imaging Spectrograph (STIS), on board the Hubble Space Telescope from July 1997 to January 2001 have been combined with FUV images to map the FUV color ratio along the STIS slit. Spatially resolved spectra of the aurora carried at similar to12 Angstrom resolution have been used to determine the amount of methane absorption as measured by the FUV color ratio of the Io magnetic footprint and its trailing tail. It is found that the absorption is systematically less than in the main polar aurora, indicating a higher altitude source region. The color ratio of the north tail is shown to slowly decrease downstream from the footprint. The combination of these spectral data with a two-stream model of the interaction of energetic electrons with the Jovian thermosphere indicates that the mean energy of the electrons creating the north FUV emission ranges from similar to55 keV at the Io footprint to similar to40 keV, 20 degrees downstream in the tail. In parallel, the incident electron energy flux drops by a factor similar to6 over the same angular distance. These observations are consistent with the steady state slippage picture where the subcorotating flux tube is accelerated very slowly up to corotation owing to the nonideal coupling. It is argued that small deviations from corotation can supply sufficient energy to fuel the observed auroral emissions. It is suggested that the parallel electric field accelerating electrons out of the flux tube only moderately depends on the time elapsed since the contact with Io, although the mapping between a point in the tail and Io is very uncertain in the presence of magnetic field line slippage.
Gustin, Jacques ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP)
Grodent, Denis ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP)
Delamere, P.
Clarke, J. T.
Language :
English
Title :
Excitation of the FUV Io tail on Jupiter: Characterization of the electron precipitation
Publication date :
November 2002
Journal title :
Journal of Geophysical Research. Space Physics
ISSN :
2169-9380
eISSN :
2169-9402
Publisher :
Amer Geophysical Union, Washington DC, United States
Acuña, M. H., F. M. Neubauer, and N. F. Ness, Standing Alfvén wave current system at Io: Voyager 1 observations, J. Geophys. Res., 86, 8513, 1981.
Belcher, J. W., et al., Plasma observations of the Alfvén wave generated by Io, J. Geophys. Res., 86, 8508, 1981.
Clarke, J. T., et al., Far-ultraviolet imaging of Jupiter's aurora and the Io "footprint", Science, 274, 404, 1996.
Clarke, J. T., et al., Hubble Space Telescope imaging of Jupiter's UV aurora during the Galileo orbiter mission, J. Geophys. Res., 103, 20,217, 1998.
Clarke, J. T., et al., Ultraviolet emissions from the magnetic footprints of Io, Ganymede, and Europa on Jupiter, Nature, 415, 997, 2002.
Connerney, J. E. P., et al., Images of excited H3+ at the foot of the Io flux tube in Jupiter's atmosphere, Science, 262, 1035, 1993.
Crary, F. J., On the generation of an electron beam by Io, J. Geophys. Res., 102, 37-49, 1997.
Delamere, P. A., H. C. Stenbaek-Nielsen, D. W. Swift, and A. Otto, Momentum transfer in the Combined Release and Radiation Effects Satellite plasma injection experiments: The role of parallel electric fields, Phys. Plasmas, 7, 3771, 2000.
Dois, V., J. C. Gérard, V. Clarke, J. Gustin, and D. Grodent, Diagnostics of the Jovian aurora deduced from ultraviolet spectroscopy: Model and GHRS observations, Icarus, 147, 251, 2000.
Drossart, P., B. Bézard, S. K. Atreya, J. Bishop, J. H. Waite Jr., and D. Boice, Thermal profiles in the auroral regions of Jupiter, J. Geophys. Res., 98, 18,803, 1993.
Frank, L. A., and W. R. Paterson, Intense electron beams observed at Io with the Galileo spacecraft, J. Geophys. Res., 104, 28,657, 1999.
Frank, L. A., et al., Plasma observations at Io with the Galileo spacecraft, Science, 274, 394, 1996.
Gérard, J. C., and V. Singh, A model of energetic electrons and EUV emission in the Jovian and Satumian atmospheres and implications, J. Geophys. Res., 87, 4525, 1982.
Goertz, C. K., Io's interaction with the plasma torus, J. Geophys. Res., 85, 2949, 1980.
Goldstein, M. L., and J. T. Thieman, The formation of arcs in the dynamic spectra of Jovian decameter burst, J. Geophys. Res., 86, 8569, 1981.
Grodent, D., J. H. Waite Jr., and J. C. Gérard, A self-consistent model of the Jovian auroral thermal structure, J. Geophys. Res., 106, 12,933, 2001.
Gustin, J., D. Grodent, J. C. Gérard, and J. T. Clarke, Spatially resolved far ultraviolet spectroscopy of the Jovian aurora, Icarus, 156, 91, 2002.
Mauk, R. H., B. J. Anderson, and R. M. Thorne, Magnetosphere-ionosphere coupling at Earth, Jupiter, and beyond, Comparative Aeronomy, Geophys. Monogr. Ser, vol. 130, edited by M. Mendillo, A. Nagy, and J. H. Waite, AGU, Washington, D.C., 2002.
Neubauer, F. M., Nonlinear standing Alfven wave current system at Io: Theory, J. Geophys. Res., 85, 1171, 1980.
Nishida, A., and Y. Watanabe, Joule heating of the Jovian ionosphere by corotation enforcement currents, J. Geophys. Res., 86, 9945, 1981.
Prangé, R., D. Rego, L. Pallier, J. Connerney, P. Zarka, and J. Queinnec, Detailed study of FUV Jovian auroral features with the post COSTAR Hubble Faint Object Camera, J. Geophys. Res., 103, 20,195, 1998.
Russell, C., and D. Huddleston, The unipolar inductor myth: Mass addition or motional electric field as the source of field-aligned currents at Io, Adv. Space Res., 26, 1665, 2000.
Saur, J., F. M. Neubauer, D. F. Strobel, and M. E. Summers, Three-dimensional plasma simulation of Io's interaction with the Io plasma torus, J. Geophys. Res., 104, 25,105, 1999.
Schinder, K., M. Hesse, and J. Bim, Magnetic field-aligned potentials in nonideal plasma flow, Astrophys. J., 380, 293, 1991.
Waite, J. H., Jr., T. E. Cravens, J. U. Kozyra, A. F. Nagy, S. K. Atreya, and R. H. Chen, Electron precipitation and related aeronomy of the Jovian thermosphere and ionosphere, J. Geophys. Res., 88, 6143, 1983.
Wilkinson, M. H., Evidence for periodic modulation of Jupiter's decametric radio emission, J. Geophys. Res., 103, 19,985, 1998.
Williams, D. J., R. M. Thorne, and B. Mauk, Energetic electron beams and trapped electrons at Io, J. Geophys. Res., 104, 14,739, 1999.